The present invention relates generally to multipath storage systems and, more particularly, to nondisruptive data migration and I/O load balancing over multipath connections by running a virtual switch across storage systems and multipathing among storage and server.
According to recent trends, a new multipath networking method known as TRILL (Transparent Interconnection of Lots of Links) is under standardization process for networking over Layer 2 (L2) Ethernet. TRILL allows L2 network to establish two parallel data transfer paths that have not been allowed in traditional Ethernet based on STP (Spanning Tree Protocol). When TRILL is set up and ready in a storage network, data transfer between server and storage will be performed through multiple paths.
FIG. 1 is an example of a conventional storage area network topology. A server computer 300 is coupled to a switch 200A, which is coupled to switches 200B and 200C in parallel, which are coupled to a switch 200D, which is coupled to a data storage 200. Data transfer from/to server to/from storage is executed through a path 300-200A-200B-200D-100 and 300-200A-200C-200D-100 in parallel. In this case, there may be a performance bottleneck at the network port 210A of the switch 200D or the network port 110 of the data storage 100 that cannot handle too much traffic received through both of the paths.
In addition to L2 networking, another problem is that I/O service interruption happens through data migration beyond storage systems. FIG. 2 is an example of a conventional logical configuration of a storage area network. A server computer 300 mounts one or more logical units 530 served by a storage system 100A. An operating system running on the server 300 recognizes the logical units 530 by a network port 110A identified by its network address (MAC Address, FCID) or WWN (World Wide Name). If an administrator tries to migrate a logical unit 530 from the network port 110A to a port 110B, a server operating system must stop I/O process to suspend the static data image stored in the logical unit, and to re-mount a new logical unit through the destination network port 110B. However, a mission critical application or a business critical application running at an Enterprise Datacenter cannot be suspended while keeping its business stability.
The same problem arises when a logical unit is to be migrated beyond the storage system boundary, for instance, from the port 110A of one storage system 100A to a port 110C of another storage system 100B. It requires data copy operation among systems, so that the I/O suspension time will be longer than internal LU migration. Furthermore, an additional problem of traditional single path network is that I/O service could be interrupted after the removal of the storage system 100A because the network path must be reset onto the new data storage device.